1. Field of the Invention
The present invention relates to a chain having sliding plates that are slidably guided by a chain guide.
2. Description of the Related Art
Generally, power transmission mechanisms of cars or industrial machines and the like, or, conveyors and the like, are provided with a transmission device that transmits power via a chain passing over a drive sprocket and a driven sprocket. For example, a car engine is equipped with a timing drive system that transmits power via a chain passing over a crank sprocket (drive sprocket) and a cam sprocket (driven sprocket). This chain is slidably guided by a chain guide.
As one of conventional chains that have sliding plates slidably guided by a chain guide, one that is formed of substantially oval outer plates and inner plates having parallel upper end faces and lower end faces is known, wherein the upper end face of the outer plates is positioned lower than the upper end face of the inner plates when the outer plates and inner plates are arranged such that the pitch lines connecting the centers of their pin holes and bushing holes are straight and horizontal (see, for example, Japanese Patent Application Laid-open No. 2003-176853).
In this chain described in Japanese Patent Application Laid-open No. 2003-176853, since the upper end face of the plates that slide on the chain guide is formed straight, the sliding area between the chain guide and each plate is large, and the friction loss is large because of high sliding resistance when the chain runs. When used for a timing drive system, for example, the chain could cause a large power loss of the car engine and reduce fuel economy.
As one of the chains designed to solve the problem of friction loss described above, one that has plates with a convexly curved end face on the side where they are slidably guided by a chain guide is known (see, for example, Japanese Patent Application Laid-open No. 2008-025744).
Since the chain described in Japanese Patent Application Laid-open No. 2008-025744 is formed of plates 130 that have a convexly curved guide-side end face 131 as shown in FIG. 5, the sliding area between the plate 130 and the chain guide G is reduced, which in turn reduces the friction resistance when the chain runs, as well as provides the effects described below.
Namely, in the chain described in Japanese Patent Application Laid-open No. 2008-025744, as shown in FIG. 5, during the running of the chain, the lubricating oil L between the plate 130 and the chain guide G moves from the wider gap between the chain guide G and a front portion in the chain running direction of the plate 130 into the confined gap between the chain guide G and a portion near the apex of the guide-side end face 131, so that a Couette flow is generated due to the wedge effect. This creates a dynamic pressure that causes the chain guide G and the plate 130 to move away from each other, and the friction resistance when the chain runs can thus be reduced.
The wedge effect mentioned above is an effect of creating a pressure, i.e., a load bearing capacity, by a fluid having viscosity (lubricating oil) drawn into a wedge-shaped gap reducing in size toward the direction of motion (“Lubrication Terminology” P25: Japan Society of Lubrication Engineers, Jul. 20, 1981). The Couette flow mentioned above is a flow created in a fluid filled between two flat parallel plates when one of the plates is moved relative to the other that is kept stationary (“Dictionary of Science & Technology” P387: Editorial Board of Dictionary of Science & Technology, Tokyo University of Science, Mar. 28, 1996).